Background

Soy is a subtropical plant, native to southeastern Asia. This member of the pea family grows from one to five-feet tall and forms clusters of three to five pods, each containing two to four beans per pod. Soy has been a dietary staple in Asian countries for at least 5,000 years, and during the Chou dynasty in China (1134-246 B.C.), fermentation techniques were discovered that allowed soy to be prepared in more easily digestible forms such as tempeh, miso, and tamari soy sauce. Tofu was invented in 2nd-Century China.

Soy was introduced to Europe in the 1700s and to the United States in the 1800s. Large-scale soybean cultivation began in the United States during World War II. Currently, Midwestern U.S. states produce approximately half of the world's supply of soybeans.

Soy contains protein, isoflavones, and fiber, all thought to provide health benefits. Soy is an excellent source of dietary protein, including all essential amino acids. Soy is also a source of lecithin or phospholipid. Soy isoflavones and lecithin have been studied scientifically for numerous health conditions. Isoflavones such as genistein are believed to have estrogen-like effects in the body, and as a result are sometimes called "phytoestrogens."

Soy protein has also been investigated for benefit in terms of heart disease risk factors, reducing menopausal symptoms, weight loss, arthritis, brain function, and exercise performance. Dietary soy may decrease the risk of breast cancer in women and prostate cancer in men, as well as other types of cancers. In general, the supportive evidence for use of phytoestrogens as treatments for menopause, heart disease, bone disease, weight loss, and cancer is limited. The use of soy formula has been investigated in the treatment of diarrhea in infants and is an effective and safe alternative to cow's milk formula in most infants.

Dosing

The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.

Adults (over 18 years old)

Soy protein dosing is controversial and consistent clinical effects have been lacking. In the United States, 25 milligrams daily of soy has been approved for decreasing cholesterol. Incidence of breast and prostate cancer is low in Asia, therefore dietary soy intake has been investigated.

As an antioxidant, 25 grams of soy protein in a single shake has been taken by mouth for up to eight weeks and 50 grams of soy (kinako) has been used daily for 90 days.

For cancer (prevention and treatment), 20-58 grams of soy protein for six weeks to six months has been taken by mouth; also 8 ounces of soymilk has also been taken three times daily for 12 months.

For heart health, 25-50 grams of soy protein (e.g. Abalon®), and soy-containing foods (such as tofu and yogurt), and soy foods with 40-60mg isoflavones have been taken by mouth daily for 4-52 weeks.

For gallstone prevention, soy protein has been taken by mouth for two weeks.

For cognitive function, 25.6 grams or an unknown dose of soy protein, soy supplement, or soymilk (containing 60-160mg isoflavones) have been taken by mouth daily for 3-12 months.

For Crohn's disease, soya-derived protein has been added to standard enteral treatment for four weeks.

For cyclical breast pain, 17 grams of soy protein as a beverage has been taken by mouth twice daily for three months.

For diabetes, 11.3-111 grams of soy protein or 0.5-0.8 grams per kilogram soy protein (e.g. Abalon®) has been taken by mouth daily for periods of four weeks to four years. Also, fermented soybean touchi tea has been taken by mouth for three months, a single dose of 7-10 grams of soy fiber or a meal with 10 grams soy polysaccharide has been used as a single dose; 52 grams of soy hull fiber has been taken by mouth daily for four weeks; and a soy protein diet has been followed for eight weeks.

For enhancement of exercise performance, 0.4-1.5 grams per kilogram of soy protein divided has been used once to three times daily for 6-8 weeks; and a fat-free soy protein drink has been taken by mouth twice daily post-exercise, five days weekly for 12 weeks.

For fibromyalgia, a shake with 20 grams of soy protein and 160 milligrams of soy isoflavone has been taken by mouth daily for six weeks.

For high blood pressure, 15-66 grams of soy protein has been taken by mouth daily for 4-52 weeks; also 500 milliliters of soymilk has been taken twice daily for three months.

For inflammation due to hemodialysis, soy protein has been taken by mouth for eight weeks.

For iron deficiency anemia, two capsules of shoyu polysaccharides has been taken by mouth twice daily for four weeks.

For kidney disease, the following diets have been followed for seven weeks to six months: a soy-based vegetable low-protein diet; a 35% soy protein and 30% vegetable protein diet; a diet with soy protein as half of the daily protein intake.

For lowering cholesterol, 11.3-140 grams of soy protein has been taken by mouth daily for 3-52 weeks.

For the menopausal symptom hot flush, 33.3-134.4 milligrams of soy supplement, extract, or protein has been taken by mouth daily for 12-96 weeks. Dietary soy powder (Previna®) containing 12 milligrams of soy protein and 45 milligrams of isoflavones has been taken by mouth twice daily for 16 weeks. Also, 40-134 milligrams of soy isoflavones has been taken by mouth daily for 6-26 weeks.

For non-hot flush menopausal symptoms, soy protein, soy supplement, or soymilk (containing 60-160 milligrams of isoflavones has been taken daily for 3-12 months; also a dose of 25 grams of soy protein has been used for up to 12 months.

For metabolic syndrome, soy protein has been taken by mouth for eight weeks in place of animal protein.

For motility disorders, 15 grams of soy polysaccharide fiber have been taken by mouth daily for up to 18 days.

For osteoarthritis, 40 grams of soy protein has been taken by mouth daily for three months.

For osteoporosis, 500 milliliters of soymilk has been taken daily for 1-2 years; also 80.4 milligrams to 40 grams of soy protein has been taken daily for three months to one year.

For premenstrual syndrome (PMS), 30.5 grams of soy protein isolate has been taken daily for seven months.

For rheumatoid arthritis, soy peptide has been taken by mouth for four weeks.

For skin damage, a skin cream containing soy ingredients has been applied to the skin for 12 weeks.

For spinal cord injury, 48 grams of a vanilla-flavored soy drink has been taken by mouth.

For weight loss, 15 grams of soy protein per 1,000 kilocalories has been taken by mouth daily for up to 12 weeks (as five meal replacements, three soy shakes, or soy foods); four pieces of beta-conglycin candy (0.625 grams of beta-conglycin per candy) has been taken by mouth twice daily for reduction of visceral fat; a soya-based liquid formula for two meals daily with was taken by mouth for four weeks; a soy-based low-calorie diet has been followed for eight weeks; five foods prepared with isolated soy protein have been consumed to maintain a protein intake between 86-96 grams daily for 30 days; 25 milligrams of soy isolate (containing 59% protein) or soy concentrate (containing 59.5% protein) has been taken by mouth twice daily for 12 weeks.

Children (under 18 years old)

Soy is generally considered safe for eating by infants and children according to both traditional knowledge and research. Due to potential safety concerns, a qualified healthcare provider should be consulted regarding the choice of infant formula.

For acute diarrhea in infants and young children, soy formula has been studied for up to 14 days; utilized brands included Nursoy® and Isomil®.

To prevent food allergies in infants, soy formula has been studied.

For infantile colic, various soymilk formulas (e.g. ProSobee®, Soy Enfamil®, Isomil®) have been taken for periods of 48 hours to 28 days.

For iron deficiency anemia, a 16 ounce of soy-based formula has been used daily for 12 weeks.

For lowering cholesterol levels, children took soy protein by mouth for four weeks.

For weight gain in infants, soy formula has been taken by mouth over a 6-12 month period.

Evidence

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Dietary source of protein

Soy products, such as tofu, are high in protein and are an acceptable source of dietary protein.

A

High cholesterol

Human research reports that adding soy protein to the diet can moderately decrease total cholesterol and low-density lipoprotein ("bad" cholesterol). The most benefit has been seen when all animal protein is substituted with soy, especially in soy products that contain isoflavones. The reductions in cholesterol may last as long as the diet is continued.

B

Diarrhea (acute) in infants and young children

Research reports that infants with diarrhea who are fed soy formula have less diarrhea than those fed milk formula. This only applies to children that are unable to eat solid food. Further research is needed before a conclusion can be made. Parents are advised to speak with qualified healthcare providers if their infants experience prolonged diarrhea, become dehydrated, develop signs of infections (such as fever), or have blood in the stool. A healthcare provider should be consulted for current breastfeeding recommendations and to suggest long-term formulas that provide enough nutrition.

B

High blood pressure

Research in humans generally shows that soy lowers blood pressure. Further research is needed to determine the ideal soy preparation for lowering blood pressure.

B

Menopausal symptoms (hot flush)

Research shows that soy reduces hot flash occurrence in menopausal women. Further research is needed before a strong conclusion can be made.

C

Allergies (prevention of food allergies)

Soy formulas are commonly used by infants with sensitivities to milk-based formulas. There is currently little evidence to support the use of soy formulas for preventing food allergies. Further research is needed in this field.

C

Antioxidant

There is some evidence in support of soy increasing antioxidant status in humans. In general, diets high in plant foods may offer antioxidant benefits. Further research is required in this field before conclusions can be made.

C

Bowel/intestinal disorders

The effect of soy on ulcers in the bowel/intestinal tract has been examined in limited study. Overall, the effects of soy products appear beneficial. Further study is required before conclusions can be made.

C

Cancer (prevention and treatment)

Limited human research shows that soy may decrease the risk of cancer, including breast, prostate, and colon cancer. However, confounding factors including dietary and lifestyle habits, culture, and genetics must be considered. Further research is needed before a conclusion can be made.

C

Cognitive function

It is unclear if soy supplementation in postmenopausal women can improve cognitive function. Results from studies are mixed. Further research is necessary.

C

Crohn's disease

From limited human research, it is unclear if soy helps with Crohn's disease. Further research is needed before a conclusion can be made.

C

Cyclical breast pain

Limited research shows that soy may decrease cyclical breast pain, which is pain linked to the menstrual cycle. Further research is needed to draw conclusions.

C

Diabetes

Human research demonstrates mixed results of soy products for blood sugar levels in people with type 2 diabetes. Overall, better quality research is needed in this area.

C

Exercise performance

Soy protein has been investigated as a source of protein with potential for benefit in exercise performance. In general, research findings suggest soy protein is better than a lack of protein but is unlikely to be superior to other sources of protein. Further research is required in this field.

C

Fibromyalgia

Limited evidence shows that soy lacks benefit for physical function and depression symptoms in fibromyalgia. Further research in this area is needed before any firm conclusions can be made.

C

Gallstones

There is insufficient evidence regarding the use of soy as a therapy for gallstones. Further research is needed before a conclusion can be made.

C

Heart disease

Research suggests cholesterol-lowering effects of dietary soy, which in theory, may reduce the risk of heart problems. However, in limited research soy lacked an effect on blood vessel function and increased the levels a heart disease risk marker. Further investigation is needed before a conclusion can be made.

C

Infantile colic

There is currently a lack of scientific evidence regarding the use of soy formula for fussiness and gas in infants with cow's milk allergy. Further research is warranted.

C

Inflammation

Sufficient evidence is lacking regarding the use of soy protein for inflammation associated with hemodialysis (a treatment given when kidneys fail, to remove waste from the blood). Further research is needed.

C

Iron deficiency anemia

There is currently a lack of sufficient evidence regarding the use of soy-based formula in the treatment of iron deficiency anemia in children. Further research is needed.

C

Kidney disease

Sufficient evidence is lacking regarding the use of soy in the treatment of kidney diseases, such as nephrotic syndrome. Further research is necessary. People with kidney disease should speak with their healthcare providers about the recommended amounts of dietary protein because soy is a high-protein food.

C

Menopausal symptoms (non hot-flush)

Overall, evidence suggests that soy products containing isoflavones may help reduce various menopausal symptoms. More study is needed to confirm this use.

C

Menstrual migraine

An herbal combination containing soy may help prevent menstrual migraine attacks. Further research is needed before a conclusion can be made.

C

Metabolic syndrome

Treatment with soy protein and soy nuts was evaluated in patients with metabolic syndrome. Benefits were found in terms of decreased cholesterol levels from consuming soy. Further research is required in this field to draw conclusions.

C

Motility disorders (problems with digestion)

In limited research, the addition of soy polysaccharide to non-regular diets improved stool consistency. It is unclear if soy polysaccharide would be superior to other fiber sources in this regard. Further research is warranted.

C

Osteoarthritis

Osteoarthritis is a form of arthritis caused by the breakdown of cartilage and resulting in symptoms of pain and decreased range of motion of joints. Early research suggests that intake of soy protein may be associated with reduced symptoms of osteoarthritis. Further research is needed before conclusions can be made.

C

Physical functioning and well-being in the elderly

Early evidence suggests that increased dietary intake of soy is associated with a decreased risk of physical disability in healthy older women. Further high quality research is needed for conclusions to be made.

C

Premenstrual syndrome (PMS)

Sufficient evidence is lacking regarding the use of soy in managing symptoms of PMS. Further high-quality clinical research is needed in this area before any firm conclusions can be made.

C

Rheumatoid arthritis

There is currently insufficient evidence regarding the use of soy as a treatment for rheumatoid arthritis. High-quality clinical research is needed in this area.

C

Skin aging

Research shows that combination products containing soy extract have demonstrated improvements in wrinkles and skin quality. More research is needed with soy products alone before a conclusion can be made.

C

Skin damage caused by the sun

A soy moisturizing cream may help improve signs of sun damage, including discoloration, blotchiness, dullness, fine lines, and overall texture. Because the cream contained other ingredients besides soy, more research with soy alone is needed.

C

Spinal cord injury

Whey protein has traditionally been used as a protein source to increase body strength. Limited research investigated whether soy protein could be used to increase walking performance in patients with incomplete spinal cord injury. Further research is needed to make a conclusion.

C

Thyroid disorders

Early research suggests that soy supplements lack an effect on thyroid function. More research is needed.

C

Tuberculosis

According to early research, soy may improve tolerance of antimicrobial drugs that are used to treat tuberculosis. Further research is needed to make conclusions.

C

Weight gain (infants)

In limited study, weaning infants with cow's milk allergy to soy based formula resulted in reduced weight for age as compared with formulas containing hydrolyzed (broken down) proteins. Further research is required in this field.

C

Weight loss

Some research suggests that soy might be as effective as skim milk and more effective than a low-calorie diet alone in reducing weight. Other research has reported conflicting results. Further research is needed before a conclusion can be made.

F

Osteoporosis

Human research shows that soy lacks an effect on bone mineral density in post-menopausal women and healthy adults. However, more research is needed.

Uses based on tradition or theory

The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Interactions

Interactions with Drugs

Soy may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants ("blood thinners") such as warfarin (Coumadin®) or heparin, anti-platelet drugs such as clopidogrel (Plavix®), and non-steroidal anti-inflammatory drugs such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).

Soy may lower blood sugar levels. Caution is advised when using medications that may also lower blood sugar. People taking drugs for diabetes by mouth or insulin should be monitored closely by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.

Soy may cause high blood pressure. Caution is advised in people taking drugs that affect blood pressure.

Soy may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system. As a result, the levels of these drugs may be increased in the blood, and may cause altered effects or potentially serious adverse reactions. People using any medications should check the package insert, and speak with a qualified healthcare professional, including a pharmacist, about possible interactions.

Because soy contains estrogen like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.

Interactions with Herbs and Dietary Supplements

Soy may increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.

Soy may lower blood sugar levels. Caution is advised when using herbs and supplements that may also lower blood sugar. People taking drugs for diabetes by mouth or insulin should be monitored closely by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.

Soy may cause high blood pressure. Caution is advised in people taking herbs and supplements that affect blood pressure.

Soy may interfere with the way the body processes certain herbs or supplements using the liver's "cytochrome P450" enzyme system. As a result, the levels of other herbs or supplements may be altered in the blood. It may also alter the effects that other herbs or supplements possibly have on the P450 system.

Because soy contains estrogen like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.

Note: Ipriflavone, a synthetic isoflavone, has been studied as a possible way to treat or prevent bone loss in post-menopausal women. This monograph concentrates on natural soy. Ipriflavone is discussed separately. Soy isoflavones, genistein and daidzein, have been studied as treatments for various conditions. This monograph concentrates on soy protein or foods containing soy protein. Isoflavones are discussed separately. Soy lecithin is derived from the processing of soybeans. It is a mixture of fatty substances separated from soybean oil and used as a food additive. Its chemical name is phosphatidylcholine and contains the constituents of choline, phosphoric acid, glycerin, and fatty acids. Soy lecithin is discussed in a separate monograph. Soybean oil and soy-derived sterols are not specifically discussed.

Safety

The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

Allergies

Avoid with a known allergy to soy, any of its parts, or members of its plant family.

Soy may act as a food allergen similar to milk, eggs, peanuts, fish, and wheat. Symptoms of an allergic reaction range from a runny nose, to inflammation of the digestive tract to a sudden drop in blood pressure.

Side Effects and Warnings

Soy is likely safe when used in the diet in adults, children, and infants, although maximum duration is unknown. Soy protein has been safely used for up to one year. Soy formula has been safely used in full-term infants.

Use cautiously in people with hormone-sensitive cancers such as breast, ovarian, or uterine cancer, or hormone-sensitive conditions such as endometriosis.

Soy may increase the risk of bleeding. Caution is advised in people with bleeding disorders or taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary.

Soy may lower blood sugar levels. Caution is advised in people with diabetes or low blood sugar, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood sugar levels may need to be monitored by a qualified healthcare professional, including a pharmacist, and medication adjustments may be necessary.

Soy may cause high blood pressure. Caution is advised in people taking drugs or herbs and supplements that alter blood pressure.

Because soy contains estrogen like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.

Soy may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system.

Use cautiously in people who have anemia, cystic fibrosis, or disorders of the thyroid, stomach, intestine, immune system, or heart.

Avoid with a known allergy to soy, any of its parts, or members of its plant family.

Avoid soy at levels higher than normally consumed in food if the person is pregnant or lactating, has cancer or is at risk for cancer, or is taking medications.

Pregnancy and Breastfeeding

Soy as a part of the regular diet is traditionally considered to be safe during pregnancy and breastfeeding, although scientific research is limited in these areas.

Recent study demonstrates that isoflavones are transferred through breast milk from mothers to infants. In non-human study, high doses of isoflavones resulted in tumors and reproductive changes in offspring. Avoid high doses of soy or soy isoflavones in humans.

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